1. Field of the Invention
The present invention relates to a blasting apparatus and a blasting method for ejecting blasting media to a surface to be treated and roughening the surface to be treated to perform surface preparation.
2. Description of the Related Art
In the suppression chamber of an atomic power plant facility, the frame is made of concrete, and a pool is constructed by pasting steel plates on its inner wall surface and bottom surface. The outer surface of the steel plates, namely the inner surface of the suppression chamber is coated by recoating it with a plurality of coating materials excellent in corrosion resistance, decontaminability and the like. The repainting construction is carried out with about 10 years after the start of operation as a guide, and as a pre-construction of the repainting construction, a blasting operation of grinding the coating film including radioactive substances on the inner surface and roughening the coated surface to perform surface preparation is performed.
The blasting operation is performed by a sand blasting technique as described in Japanese Patent Application Laid-Open No. 9-109029. The sand blasting technique is a technique of causing a blast material such as sand ejected from a nozzle by high speed air to collide against a coated surface and grinding the coating film on the coated surface with the impact force to roughen the surface.
However, in the sand blasting technique, the blast material rebounds with a strong force, and therefore, there is the problem of scattering of dust particles. There is also the disadvantage that a worker who operates a nozzle has to be heavily equipped to protect his or her body from the blast material that rebounds with a strong force, which impairs workability. Further, it is difficult for the worker to perform the operation with uniform quality because he or she has a poor view due to scattering dust particles.
Thus, in order to solve such problems, the applicant of the present application proposes a technique of using a blast medium in a sponge piece form with abrasives contained in a porous elastic body, namely, a sponge blasting technique.
According to the sponge blasting technique, when a sponge blast medium ejected from a nozzle with high speed air collides against a coated surface, the blast medium becomes flat, and the contained abrasives directly collide against the coated surface at a high speed. Thereby, the coating film can be ground and removed as in the sand blasting technique. Dust particles which usually float in the air are taken into the sponge pieces and directly drop, and therefore, there is the advantage of being capable of reducing scattering of dust particles. Further, since the repulsive force is also absorbed by the sponge pieces, rebound is drastically reduced, and thereby, there is provided the advantage that the worker who operates the nozzle can be lightly equipped.
Incidentally, roughness of the roughened coated surface of the suppression chamber is specified in accordance with the coating material to be coated. Therefore, a worker selects the abrasive of the material corresponding to the roughness, and the worker treats the coated surface to desired roughness as the worker manually repeats the blasting operation and roughness measurement.